Understanding Combustion Safety-Valve Standards and Regulations (2023)

As a design engineer responsible for developing and specifying boilers, dryers, furnaces, heaters, ovens and other industrial heating equipment, you face a daunting labyrinth of standards and industry regulations. Regulatory bodies sound a bit like alphabet soup, with acronyms like UL, FM, CSA, UR, AGA, ASME, ANSI, IRI, CE and NFPA tossed about. This article will help explain a common task for many thermal processing equipment specifiers: meeting the requirements of key codes — including Underwriters Laboratories (UL), Factory Mutual Insurers (FM) and the National Fire Protection Association (NFPA) — for safety valve equipment used in process heating applications.

Click here to see the Valves Codes & Standards table.

Ensuring Safety via High Reliability Valves

Key to designing safety into your fuel train configurations are familiar technologies such as safety shutoff valves and vent valves as well as visual-indication mechanisms and proof-of-closure switches.

Your design skills come into play with how you take advantage of the wide range of products available. You can mix and match solenoid and safety shutoff valves — within designs from catalytic reactors to multi-zone furnaces — to create easily installed, cost-effective solutions that comply with all necessary standards. (See table.)

Make sure, however, that you start with a good grasp of valve element fundamentals. For example, examining a proof-of-closure (POC) switch underlines how reliably modern valves can ensure combustion safety. The POC unit provides an electrical contact interlocked with the controller safety circuit. In a typical design, the switch is located at the bottom of the valve, positioned to trace the stroke of the valve disc. When the disc seal reaches the fully closed position, it triggers the mechanism to push down on the contact, closing it and triggering the unit’s visual indicator to show open or closed status. As a result, the operator can act with full confidence in situations where it is critical that a safety valve be safely closed.

(Video) Siemens Gas Valves; Safety Shutoff and Control

To provide ease of installation, many users prefer valves with modular capabilities. For example, to reduce mounting complexity, you can choose modular gas safety shut-off valves — combining a solenoid valve with an electrohydraulic motorized valve for a compact double-valve footprint, a slow-open feature and high flow rates. An accompanying actuator can provide on/off or high/low/off firing rates as well as visual indication and proof of closure for compliance with most industry standards.

Also, you may want to look for valves that include useful features such as pipe taps, which can facilitate accurate pressure readings and leakage testing.

High reliability valve components like these are available to meet a many standards, including those shown in the sidebar.

Knowing your valve choices — and how they meet given codes and standards — can reduce the time required for design and production while facilitating compliance. This results in safer, more efficient and cost-effective heating process installations.

Chart

Valve Codes and Standards: Typical Fuel-Train Installation Sizes

Under 150,000 BTU/hr

NFPAFor fluid heaters under 150,000 BTU, NFPA requires two safety shutoff valves.

(Video) [Energy | Combustion] Safety Shutoff Valve Leak Test Demonstration

Under 400,000 BTU/hr

FMFor installations in this range, FM requires one safety shutoff valve equipped with visual indication. This covers several types ofequipment under several standards: Gas-fired, single-burner boilers and furnaces; space heaters, including unit, radiant, duct furnace,makeup air and rooftop types; and industrial ovens and dryers. Valves should be approved for FM Class 7400 liquid and gas safety shutoff.

NFPAFrom 150,000 to 400,000 BTU, NFPA mandates two safety shutoff valves equipped with visual indication. For furnaces of 150,000 BTU ormore, it requires two safety shutoff valves equipped with visual indication. NFPA does not cover boilers in this category.

From 400,000 to 2,500,000 BTU/hr

ULUL requires two safety shutoff valves or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This coversgas burners, heating furnaces and boilers (except process equipment).

FMFor relevant units except industrial ovens and dryers, FM requires two safety shutoff valves equipped with visual indication or one safetyshutoff valve equipped with visual indication and a proof-of-closure switch. It mandates the above choice (two safety shutoff valves equippedwith visual indication, or one safety shutoff valve equipped with visual indication and a proof-of-closure switch), also for space heaters,including unit, radiant, duct furnace, makeup air and rooftop types. Valves should be approved for FM Class 7400 liquid and gas safety shutoff.However, for industrial ovens and dryers, FM follows NFPA.

NFPANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and aproof-of-closure switch. This also applies to furnaces, and it mandates position indication for safety shutoff valves to burners or pilots. NFPAdoes not cover boilers in this category. For fluid heaters over 400,000 BTU, NFPA mandates one safety shutoff valve equipped with visualindication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch.

From 2,500,000 to 5,000,000 BTU/hr

ULUL requires two safety shutoff valves or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. This coversgas burners, heating furnaces and boilers (except process equipment). Valves are certified as UL429 electrically operated valves.

(Video) Pressure Safety Valves, Operation and Testing - sample

FMFor relevant units, except industrial ovens and dryers, FM requires two safety shutoff valves equipped with visual indication or onesafety shutoff valve equipped with visual indication and a proof-of-closure switch. This covers gas-fired, single-burner boilers andfurnaces and space heaters — including unit, radiant, duct furnace, makeup air and rooftop types. Valves should be approved for FMClass 7400 liquid and gas safety shutoff. For industrial ovens and dryers, however, FM follows NFPA.

NPFANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and aproof-of-closure switch. This also applies to furnaces, and mandates position indication for safety shutoff valves to burners or pilots. NFPAdoes not cover boilers in this category.

From 5,000,000 to 12,500,000 BTU/hr

FMFor gas-fired, single-burner boilers and furnaces, FM requires one safety shutoff valve equipped with visual indication and onesafety shutoff valve equipped with visual indication and a proof-of-closure switch. This covers gas-fired, single-burner boilersand furnaces and space heaters — including unit, radiant, duct furnace, makeup air and rooftop types. It also mandates positionindication for safety shutoff valves to burners or pilots. Valves should be approved for FM Class 7400 liquid and gas safety shutoff.For space heaters, including unit, radiant, duct furnace, makeup air and rooftop types, FM mandates two safety shutoff valves equippedwith visual indication or one safety shutoff valve equipped with visual indication and a proof-of-closure switch. For industrial ovens anddryers, FM follows NFPA.

NFPANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication and aproof-of-closure switch. This also applies to furnaces and it mandates position indication for safety shutoff valves to burners or pilots. NFPAdoes not cover boilers in this category.

More than 12,500,000 BTU/hr

ULUL requires one safety shutoff valve, one safety shutoff valve equipped with visual indication and a proof-of-closure switch and one ventvalve. This covers gas burners, heating furnaces and boilers (except process equipment). Valves are certified as UL429 electrically operatedvalves.

FMFor gas-fired, single-burner boilers and furnaces, FM requires two safety shutoff valves equipped with visual indication and proof-ofclosureswitches. It also mandates position indication for safety shutoff valves to burners or pilots. Valves should be approved for FM Class7400 liquid and gas safety shutoff.

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FM con'tFor space heaters, including unit, radiant, duct furnace, makeup air and rooftop types, FM mandates one safety shutoff valve equippedwith visual indication and one safety shutoff valve equipped with visual indication and a proof-of-closure switch. FM also requires thisarrangement for industrial ovens and dryers.

NFPANFPA requires one safety shutoff valve equipped with visual indication and one safety shutoff valve equipped with visual indication anda proof-of-closure switch. This also applies to furnaces and it mandates position indication for safety shutoff valves to burners or pilots.For both single-burner and multiple-burner boilers, NFPA requires two safety shutoff valves equipped with visual indication and proof-ofclosureswitches and one vent valve.

FAQs

Is standard for pressure safety valve? ›

Safety valves may be installed on pressure vessels, boilers, gas storage tanks and in piping systems. The standards for safety valves are API 526 or ASME.

What are the requirements for safety valve placement on a boiler? ›

Safety or relief valves shall be installed at the top of the boiler with the spindle of the valve in an upright vertical position. The inlet and discharge piping shall be as short and direct as possible.

Why do boilers have 2 safety valves? ›

SThe safety valve is the most important safety fitting as it is fitted to prevent excessive pressure buildup in the boiler. Excessive pressure can lead to the boiler explosion. According to FMA regulation 1970, every boiler having a heating surface surpassing 100 square feet must be equipped with two safety valves.

What is SSOV valve? ›

While there are many safety devices required by codes and standards to ensure the safe operation of fuel-fired heating equipment, the safety shutoff valve (SSOV) serves as a key safety control device to prevent the flow of gas or oil into the combustion chamber when the equipment is shutdown or an abnormal condition ...

What does API 598 mean? ›

API Standard 598, from the American Petroleum Institute, provides industry standards for valve ratings and valve leakage. The standard is currently in the 9th edition, which was released in 2009.

How many types of safety valves are there? ›

There are two main types of safety valves. Spring loaded safety valves and pilot operated safety valves.

What is the maximum set pressure for safety valve? ›

The safety valves shall be reset at a pressure at least 2.5% below, but not more than 5% below the safety valve set pressure. The 5% limit is increased to 10% for valves having a body seat bore less than 32 mm and/or having a set pressure of 2 bar gauge or less.

At what PSI is the safety valve set to open? ›

Safety relief valves shall be set to open at pressures not exceeding 6 psi above the MAWP.

How do you calculate set pressure on a safety valve? ›

For example, if the safety valve overpressure was 25% and the percentage MAAP was only 10%, making the set pressure equal to the MAWP means that the relieving pressure would be 15% greater than the MAAP. In this instance, the correct set pressure should be 15% below the MAWP.

Why boiler safety valve lift is D 4? ›

Area of valve bore = area of escape i.e the valve circumference X lift; Neglecting area taken by the valve prongs. To give greater lift than D/4, is unnecessary, this gives the full equivalent area. Excessive lift results in shock or hammering thus the fatigue will take place.

What is the most important valve on a boiler? ›

The safety valve is the most important safety device in a boiler or domestic hot-water system. It is designed to relieve internal pressure if a range of failures occur within the system.

What is the difference between relief valve and safety valve? ›

Relief valves are designed to help your facility avoid system failures, and protect equipment from overpressurized conditions. The term safety valve, on the other hand, refers to pressure valves that are designed to protect people, property, and processes.

How many air changes should occur during Prepurge? ›

(1) Prepurge. Boilers must undergo a continuous purge of the combustion chamber and convecting spaces to make sure of a minimum of 5 changes of air. The purge must not be less than 15 seconds in duration, and must occur immediately prior to the trial for ignition of the initial burner of a boiler.

What is a seismic shut-off valve? ›

Earthquake natural gas shut-off valve (also known as a seismic natural gas shut-off valve) automatically shuts off your natural gas service when an earthquake of a sufficient magnitude occurs at your home.

What is the other name for the shut off valves? ›

A shut off valve might also be referred to as a lock out valve, cut off valve, a shutdown valve, an emergency shutdown valve, a ball valve, or an exhausting ball valve.

Is code for pressure relief valve? ›

API 521 Standard:

In simple words this standard caters towards selection of pressure relief device (Relief valves, Rupture disk, their combinations etc) based on various process scenarios.

What is PSV and PRV? ›

Both pressure relief valves (PRV) and pressure safety valves (PSV) are used for process safety to relieve excess pressure. Although they're often used interchangeably, they do have different functions and it's important to know the difference.

Which safety valve is used on high pressure boilers? ›

Pilot - operated relief valves are used in the high pressure and low pressure boiler.

Are all pressure relief valves the same? ›

Most valves are rated at 150 psi and 210° F, but their capacity ratings vary greatly. Sometimes, an additional T&P relief valve with a lower temperature and pressure rating (typically 180° and 100 psi) is installed in a plastic hot-water distribution system to protect the piping system itself.

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